Eight bytes of scratch. The sprite routines only know how to draw from a record, so anything that has to appear without being a creature -- the lives on the scroll, the pictures on the title screen -- is written in here first and drawn from here.

That it is eight bytes and not sixteen is the useful part. A monster's record is sixteen, but only its first eight describe the thing itself: sprite, room, a flag, x, y, drawing mode. Each half of a door or furniture record is eight bytes too. So the short form is the common one, and an actor is that plus another eight for how it moves and what it has in the air.